Closed loop control over delivery of liquid material to semiconductor processing tool

ABSTRACT

Liquid material is precisely dispensed to a semiconductor processing tool utilizing closed loop control. In one embodiment, CMP slurry material of known density is supplied from a reservoir/mixing vessel to a dispense module. The dispense module also receives a flow of an inert gas through a gas supply valve. Positive pressure arising within the dispense module due to the inert gas flow causes an outflow of slurry from the dispense module to the CMP platen. The rate of flow of the slurry to the CMP platen over time is determined by monitoring the change (decline) in weight of the filled dispense module. In a similar manner, variation in the rate of flow of slurry over time may be detected by monitoring variation in changes in weight of the filled dispense module over time. A regulator structure in electronic communication with the dispense module and with the gas supply valve receives first signals at different time points indicating the weight change of the dispense module. In response, the regulator structure communicates a second signal to the gas supply valve, reflecting an appropriate change in the rate of flow of CMP slurry material to the platen. This second signal causes the gas supply valve to vary the flow of inert gas to the dispense module in order to control changes in the flow rate of the slurry.

BACKGROUND OF THE INVENTION

The present invention relates to a method for controlling delivery ofliquid material to a semiconductor processing tool utilized insemiconductor processing.

Dispensing of slurry material to a platen of a chemical-mechanicalpolishing (CMP) tool from a delivery module is typically controlled bytimed flow of material at a rate that is generally assumed to beconstant. However, the assumption of an unvarying flow rate is often notaccurate, due to issues such as partial obstruction of valves and tubingby viscous slurry material, and uneven pumping action by pumps.

Uneven flow rates over time can lead to inaccurate dispensing of CMPslurry to the platen. Often, this problem is addressed by utilizing anoverly high flow rate to ensure that ample slurry is present on theplaten. However, oversupply of CMP slurry needlessly increases the costof the process by consuming excessive slurry material. This problem isexacerbated by the short lifetime of mixed slurry, which requires thatthe slurry be consumed shortly after its preparation from individualcomponents

It is therefore desirable that structures and methods for precisedispensing of CMP slurry material during processing be developed.

SUMMARY OF THE INVENTION

In accordance with embodiments of the present invention, dispensing ofslurry material to a CMP platen during processing is precisely meteredutilizing closed loop control. Slurry material of known density is firstsupplied from a reservoir/mixing vessel to a dispense module. Thedispense module receives a flow of an inert gas through a gas supplyvalve. Positive pressure arising within the dispense module due to theinert gas flow causes an outflow of slurry from the dispense module tothe CMP platen. The rate of flow of the slurry to the CMP platen overtime is determined by monitoring the change in weight of the filleddispense module. In a similar manner, variation in the rate of flow ofslurry over time may be detected by monitoring weight change of thefilled dispense module. A flow regulator structure in electroniccommunication with the dispense module and with the gas supply valvereceives a first signal indicating the weight change of the dispensemodule. In response, the flow regulator structure communicates a secondsignal to the gas supply valve reflecting a change in the rate of flowof CMP slurry material to the platen. This second signal causes the gassupply valve to alter the flow of inert gas to the dispense module inorder to correct for changes in the slurry flow rate.

An apparatus for dispensing material to a semiconductor processing toolin accordance with one embodiment of the present invention comprises adispense module including a first port, a second port, and a third port,the first port in fluid communication with a reservoir and the secondport in fluid communication with the semiconductor processing tool. Aload cell measures a weight of the dispense module. A gas supply valveis in communication with a pressurized inert gas supply and with thethird port of the dispense module. A flow regulator is in electroniccommunication with the load cell and in communication with the gassupply valve. The flow regulator is configured to receive a first signalfrom the load cell indicating the weight of the dispense module. Theflow regulator is also configured to transmit a second signal to the gassupply valve. The second signal changes a state of the gas supply valveto correct a rate of flow of a processing material from the dispensemodule to the semiconductor processing tool.

A method for dispensing material to a semiconductor processing tool inaccordance with one embodiment of the present invention comprisesproviding the material within a dispense module, and flowing an inertgas into the dispense module through a gas supply valve such that thematerial flows from the dispense module to the semiconductor processingtool. A flow rate of the material from the dispense module is detectedby monitoring a weight change of the dispense module. Based upon theweight change of the dispense module, a signal is generated to alter thematerial flow rate. The signal is communicated to the gas supply valveto adjust the gas supply valve to compensate for one of an excessivematerial flow rate and an insufficient material flow rate.

These and other embodiments of the present invention, as well as itsadvantages and features are described in more detail in conjunction withthe text below and the attached FIGURE.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a simplified schematic view of an apparatus for closed-loopcontrol over CMP slurry dispensing in accordance with one embodiment ofthe present invention.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

FIG. 1 shows a simplified schematic view of an apparatus for closedloopcontrol over CMP slurry dispensing in accordance with one embodiment ofthe present invention.

Closed loop CMP slurry delivery system 100 comprises dispense module 102including first port 104, second port 106, third port 108, and fourthport 109. The weight of dispense module 102 is measured by load cell110. While the weight of dispense module 102 is shown as beingdetermined by a single load cell 110, in alternative embodiments inaccordance with the present invention more than one load cell could beused for this purpose.

First port 104 of dispense module 102 is in fluid communication withslurry reservoir/mixer 112 through material supply valve 114. Secondport 106 of dispense module 102 is in fluid communication with platen116 of CMP tool 118 through on-off valve 140. Third port 108 of dispensemodule 102 is in fluid communication with pressurized inert gas supply120 through gas supply valve 122. Fourth port 109 of dispense module 102is in fluid communication with the external environment through pressurerelease valve 123.

Flow regulator 124 is in electrical communication with load cell 110,gas supply valve 122, and pressure release valve 123.

During operation of CMP tool 118, dispense module 102 is initiallyempty. The empty weight of dispense module 102 is registered by loadcell 110 and communicated to flow regulator 124.

Material supply valve 114 is opened and slurry material 126 is flowedfrom reservoir/mixer 112 through first port 104 into dispense module102. The weight of the filled dispense module 102 is then registered byload cell 110. Because the density of the slurry material is alreadyknown, the amount of slurry material present in the dispense module canreadily be precisely calculated.

Next, gas supply valve 122 is opened, and inert gas flows into thirdport 108 of dispense module 102 from inert gas supply 120. As a resultof the inflow of inert gas into dispense module 102, a positive pressureis created within dispense module 102 that in turn causes a flow ofliquid slurry material 126 from second port 106 of dispense module 102to CMP platen 116.

The rate of flow of liquid slurry material from dispense module 102 toplaten 116 of CMP tool I 18 may be determined from first timed signalssent by load cell 110 to flow regulator 124. Specifically, these signalsreflect the weight of the filled dispense module 126 at two differenttimes, such that change in weight of module 102 over a time period canbe determined by flow regulator 124.

In response to the detected change in weight of the filled dispensemodule 102, flow regulator 124 transmits a second signal to vary thestate of gas supply valve 122. Where the first signal has revealed achange in weight of the dispense module indicative of an excessiveslurry flow rate, the second signal is calculated to restrict the supplyof inert gas flowing through gas supply valve. This will in turndecrease pressure within the dispense module, reducing the rate of flowof slurry from the dispense module to the platen. Because pressure inthe dispense module may decrease only slowly in response to a restrictedinlet flow of gas, module 102 is also equipped with pressure releasevalve 123 that can be activated by flow regulator 124 to rapidly lowerthe pressure in module 102.

Conversely, where the first signal has revealed a change in weight ofthe dispense module indicative of an insufficient slurry flow rate, thesecond signal is calculated to enlarge the supply of inert gas flowingthrough gas supply valve. This will in turn increase pressure within thedispense module, elevating the rate of flow of slurry from the dispensemodule to the platen.

Where the first signal has revealed a change in weight of the dispensemodule indicative of the desired flow rate, no second signal iscommunicated to the gas supply valve, and the state of this valveremains unchanged.

Once the level of slurry present in the dispense module 102 falls belowa predetermined level 130, an alarm is sounded to indicate the necessityof refilling the dispense module 102 from slurry reservoir/mixer 112.The user may similarly be alerted where changes in the flow rate ofslurry from the dispense module indicate serious problems such asstoppages (little or no slurry flow) or leaks (excessively high slurryflow).

One important aspect of the present invention is that the actual rate ofslurry flow is continuously measured, with no assumption made as toconstant slurry flow. This approach permits precise amounts of slurry tobe delivered to the CMP tool, maximizing efficient use of this costlyconsumable material.

Precise metering of slurry flow in accordance with embodiments of thepresent invention also results in minimum delay between the transfer ofslurry from a reservoir/mixer and the actual dispensing of slurry to theCMP tool, allowing the prepared slurry to be maintained in the reservoirprior to allocation to the dispensing vessel without degradation for aminimum time period. This is important insofar as slurry materialtypically has a limited shelf life and requires mixing of its respectivecomponents shortly before being dispensed to the platen.

Another aspect of methods and structures for controlling slurry flow inaccordance with the present invention is the avoidance of use of activesensor structures to detect the rate of slurry flow.

Several varieties of active flow sensors exist, including but notlimited to paddlewheels, pressure transducers, or ultrasonic flowvelocity sensors. However, each of these sensor types poses certaindisadvantages. For example, paddlewbeels are prone to clogging due tothe high viscosity and particle count of the slurry. Ultrasonic sensorsare effective but relatively complex and expensive to operate. All typesof active flow sensors contain component parts that are subject to wearand which must be replaced periodically.

Issues relating to active flow sensors are avoided in embodiments of thepresent invention by controlling flow rates indirectly throughmonitoring weight change of the dispense module. As a result, liquiddelivery devices in accordance with embodiments of the present inventionboth more reliable and more economical than conventional liquid deliverysystems that utilize active flow sensors.

While the above is a full description of specific embodiments inaccordance with the present invention, various modifications,alternative constructions and equivalents may be used. For example,while the above description relates to an apparatus wherein the flowregulator alters the state of the gas supply valve and/or pressurerelease valve by emitting a second signal in electrical form, this isnot required by the present invention. In alternative embodiments, theflow regulator could control the state of the gas supply/pressurerelease valves pneumatically or hydraulically rather than electrically,and apparatuses and methods for dispensing liquid material would remainwithin the scope of the present invention. In such alternativeembodiments, the signal communicated from the regulator to the gassupply valve would be a change in one of air pressure, water pressure,or oil pressure where hydraulic oils are used.

In addition, while the above description relates to a closed loop methodfor dispensing a slurry material to a platen of a CMP tool, the presentinvention is not limited to this particular application. A system ormethod in accordance with embodiments of the present invention coulddeliver other liquids utilized during semiconductor processing,including but not limited to undeveloped photoresist material utilizedin lithography processes, or corrosive liquid chemicals utilized inetching processes.

Given the variety of embodiments of the present invention justdescribed, the above description and illustrations should not be takenas limiting the scope of the present invention which is defined by theappended claims.

What is claimed is:
 1. A method for dispensing material to asemiconductor processing tool, the method comprising: providing thematerial within a dispense module; flowing an inert gas into thedispense module through a gas supply valve, such that the material flowsfrom the dispense module to the semiconductor processing tool; detectinga flow rate of the material from the dispense module by monitoring aweight change of the dispense module; generating a signal to vary thematerial flow rate; and communicating the signal to the gas supply valveto adjust the gas supply valve to vary the material flow rate.
 2. Themethod according to claim 1 further comprising communicating the signalto a pressure release valve in communication with the dispense moduleand an environment, in response to an excessive material flow rate. 3.The method according to claim 1 wherein communicating the signalcomprises communicating an electrical signal to the gas supply valve. 4.The method according to claim 1 wherein communicating the signalcomprises communicating an air pressure signal to the gas supply valve.5. The method according to claim 1 wherein communicating the signalcomprises communicating a liquid pressure signal to the gas supplyvalve.
 6. The method according to claim 1 wherein providing the materialto the delivery module comprises providing chemical-mechanical polishingslurry.
 7. The method according to claim 1 wherein providing thematerial to the delivery module comprises providing undevelopedphotoresist.
 8. The method according to claim 1 wherein providing thematerial to the delivery module comprises providing wet etchantchemistry.